Frost on vehicle windows occurs due to a temperature difference between the outside and the inside of the vehicle in the winter or a rainy day. Further, a dew condensation occurs due to a temperature difference with the inside with a slope and the outside of the slope at an indoor ski resort. In order to solve the problems, heating glass was developed. The heating glass uses a concept of generating heat from a heat line by applying electricity to both ends of the heat line after attaching a heat line sheet to the glass surface or forming the heat line on the glass surface to increase a temperature of the glass surface.
The heating glass for a vehicle or architecture needs to have low resistance in order to smoothly generate the heat and should not offend the eye. For this reason, methods of preparing a known transparent heating glass, by forming a heating layer through a sputtering process of a transparent conductive material such as an indium tin oxide (ITO) or Ag thin film and then connecting an electrode to a front end, have been proposed. However, the heating glass prepared by the methods was difficult to be driven at low voltage of 40 V or less due to high surface resistance. Accordingly, for the heating at the voltage of 40 V or less, attempts are being made to use a metal line.
Meanwhile, in the known heating element, a method of controlling a heating value by a gap between the busbars was attempted, by using a pair of busbars connected with a power supply or using two pairs of busbars connected with each other in parallel. In this case, when the gap between the busbars is fixed, the surface resistance of the heating element between the busbars needs to be controlled in order to control the heating value for each part. In order to control the surface resistance of the heating element, a thickness of a conductive material constituting the heating layer is controlled or the density of a metallic pattern is controlled in the case of using the metallic pattern as a heating pattern. However, in the case where the thickness of the conductive material or the density of the heating pattern is different, there is a problem in that the heating element is easily observed due to a difference in transmittance for each part.